The present invention pertains to a hard composite cutting insert and a method of making the same. More specifically, the present invention pertains to a hard composite cutting insert that has at least two distinct regions of different material grades, as well as a method of making the cutting insert.
Hard composite cutting inserts, or hard cutting inserts, are used in conjunction with a bit body for impinging upon, and thereby disintegrating, the earth strata. Common applications that disintegrate earth strata via a cutting bit with one or more hard composite cutting inserts include road planning, coal mining and other underground mining activities, and drilling such as in the drilling of oil and gas wells.
In the case of drilling oil and gas wells, drill bits are installed at the lower end of a rotary drill string. The drill bits impinge upon the earth strata (e.g., rock and other hard formations) so as to accomplish the drilling of the bore hole for the well. These drill bits can include a tri-cone rotary drill bit such as is described and disclosed in U.S. Pat. No. 4,427,081 to Crawford. These drill bits may also include a percussion style of drill bit such as shown and described in U.S. Pat. No. 4,106,578 to Beyer. In either one of these types of drill bits, the drill bit head contains one or more apertures wherein each aperture receives its corresponding hard cutting insert. The hard cutting insert protrudes past the surface of the drill bit head to engage or impinge and disintegrate the earth strata.
Generally speaking, the hard cutting inserts are made out of cemented carbide, and more specifically, a cobalt cemented tungsten carbide. While there are a number of parameters that may vary between different grades of cobalt cemented tungsten carbide, two principle parameters are the cobalt (or binder) content and the grain size (or average grain size) of the tungsten carbide particles (i.e., hard particles). The composition of cobalt cemented tungsten carbides can also vary wherein the composition may include additives such as titanium, niobium, tantalum, vanadium, chromium and other Group IV, V or VI metals or the carbides of such metals. By varying the compositional aspects (e.g., cobalt (or binder)) content, hard carbide content, hard carbide particle size and/or the nature and extent of additives, the properties of the cemented carbide can vary. For example, the hard cemented carbide may possess a high hardness but a lower toughness or it may have a low hardness and a higher toughness.
Heretofore, some have used a dual grade hard composite cutting insert that includes two different grades of material (e.g., cobalt cemented tungsten carbide). One exemplary patent that shows a dual grade hard insert is U.S. Pat. No. 5,467,669 to Stroud. Based upon the cross-sectional views presented by FIGS. 3-6 of U.S. Pat. No. 5,467,669, it appears that one grade of material is encapsulated by another (or outer) grade of material. According to U.S. Pat. No. 5,467,669, the outer grade of material is harder and the encapsulated grade of material is tougher.
U.S. Pat. No. 5,467,669 also mentions other patents that are supposed to be dual grade inserts. These patents include U.S. Pat. No. 2,842,342 to Hagland, U.S. Pat. No. 2,888,247 to Hagland, U.S. Pat. No. 2,899,138 to Hagland, U.S. Pat. No. 4,705,124 to Abrahamson et al., and U.S. Pat. No. 4,722,405 to Langford et al.
As can be appreciated, it would be desirable to provide an improved hard composite cutting insert used in conjunction with a bit body for the purpose of impinging the earth strata wherein optimum properties for hardness and toughness can be achieved through the use of multiple grades of hard materials in one hard composite cutting insert.
It would also be desirable to provide an improved hard composite cutting insert used in conjunction with a bit body for the purpose of impinging the earth strata wherein various geometric configurations of different grades of material can be employed by the hard composite cutting insert.
Further, it would be desirable to provide an improved hard composite cutting insert used in conjunction with a bit body for the purpose of impinging the earth strata wherein different regions of different grades of material can be selectively positioned or located in the hard composite cutting insert.
In addition, it would be desirable to provide an improved method to make an improved hard composite cutting insert that achieves any one or more of the above-recited goals, and wherein the method is economical to perform.